Mason and Brady have an important guy relationship that is vital to Seasons 1 and 2. Mason and Brady seem to make fun of each other, but they like each other as close friends.
Friendship + Hatred
Mason seems to really dislike Brady. He is always insulting his ways of ruling the island, whch also applies for Boomer and Boz. In "Do Over", however, he says he and Boomer are like sons to him. Mason also seems to like tucking him and Boomer in at night, without telling them that's what he is doing. Brady also seems to sometimes like Mason, as in "Kings of Legend", he states that Mason was the person who believed in him and Boomer the most. Brady is also upset when Mason gets mad at them in the same episode. When Brady left the island, Mason is upset that he is not a king of legend. He seemed to miss Brady when he left in Season 3. Mason and Brady seem to have a father/son relationship.
Mason and Brady also seem to dislike each other. Brady and Boomer make fun of him, calling him sasquatch. Mason is also willing to hurt Brady if he hits on Mikayla, showing a little evil tension. He also threatens him and insults his way of ruling. Brady also doesn't seem to obey or keep his promises to Mason. Mason also yells at Brady and Boomer a lot.
Other than those reasons, Mason and Brady are close friends and always will be.